The objective of the proposed research are the following: 1. Developing and improving specific chemical methods for cleavage of proteins at cysteine, tryptophan, proline and selected methionine residues. 2. Use of cysteinyl and methionyl residue modifications for probing tertiary structures of proteins. 3. Exploring the use of S- cyanylation as a specific probe to evaluate the type and extent of involvement of thiol groups in enzymic catalysis. 4. Applications of chemical modification for studying the mode of action of enzymes which recognize or react with beta-lactam drugs of the penicillin and the cephalosporin types.